Welcome to Pedal Science, the weekly bike fitting blog by Nick Thomas of The Endurance Coach. This week we look at the subject of saddle height and cycling performance.
If there’s only one adjustment everyone will make when establishing their own road bike position it’s the saddle height. This is because altering saddle height is instantly noticeable and is very simple to achieve even for the most mechanically challenged person. There are several formulas and guides available based on inside leg measurement but the final position is usually determined by adjusting the height until it feels ‘about right’.
The higher the saddle the greater the amount of knee and hip extension is achieved at the bottom of the stroke: this increases the leverage (and therefore power output) up to a certain height but beyond that height overextension occurs leading to a variety of possible problems and compensations.
Establishing the correct saddle height is very subjective and ultimately dependent on the bike fitter’s opinion. However the process can become more objective if the following principle factors are taken into account:
Excessively High Saddle Position:
The higher the saddle the more extension there is in the hamstrings. Saddle height is therefore greatly affected by hamstring flexibility and the tighter the hamstrings the lower the saddle tends to be. To reduce the stretch on the hamstrings the following compensations are often observed:
Excessively plantarflexed (pointing down) feet enable the rider to reach the pedals with less knee extension. This leads to unnecessary fatigue in the calf muscles often leading to cramp. This is particularly problematic for triathletes who need the calf muscles for propulsion during the run.
Another way to avoid overextension at the knee and reach the pedals is to drop the hip as the leg passes through the bottom of the pedal stroke - this is visible from behind the rider as the hips drop from side to side. Excessive movement in the hips decreases efficiency and can also lead to lower back discomfort.
Posteriorly rotated pelvis:
As overstretched hamstrings fatigue they can gradually shorten throughout the ride. As the top of the hamstrings attach to the pelvis an obvious compensation is to rotate the pelvis back to lessen the tension in the hamstrings. The result is a slumped, hunched body position with the arms overstretched to reach the bars. The position is much less efficient and leads to reduction in sustainable power.
Lower back flexibility:
If the saddle height causes the pelvis to posteriorly rotate there is more tension in the lower back as the amount of lumbar flexion is increased. For someone with limited lower back flexibility this can result in lower, mid or upper back pain which becomes worse as the ride progresses.
Excessively Low Saddle Position:
Hip flexion range of movement (ROM):
If the saddle is too low there is less leverage, reduced power output and insufficient knee extension at the bottom of the stroke. This can lead to knee problems due to increased stress behind the patella, especially if the cyclist is prone to using big gears.
At the top of the stroke the hip flexion angle is consequently reduced which requires a certain amount of mobility in the hips to enable the leg to pass over the top. If hip flexion ROM is limited there is usually a dead spot at the top of the stroke which affects pedalling efficiency and power output. To compensate for this the following compensations are often observed:
As the foot passes over the top of the stroke the hip ‘hitches’ up to provide unrestricted movement and maintain continuity in the pedal stroke. The result is rocking hips, inefficient cycling mechanics and an increased likelihood of lower back pain.
As insufficient hip flexion ROM prevents the foot passing uninterrupted over the top of the stroke the body can avoid the dead spot and provide the necessary movement by abducting (sticking out) the knees and passing them around the pedal stroke instead. The problem is that the knees are misaligned so the patella doesn’t track properly, a common cause of knee pain, especially if the cyclist uses big gears or does a lot of climbing.
Injury history should always be taken into account when the above points are considered. For someone with a history of hamstring or calf injuries it would make sense to limit the amount of knee extension. Conversely if someone complains of knee pain they might benefit from a higher saddle to improve knee biomechanics and reduce the stress in the knees.
It’s questionable whether a generic chart or formula will provide the most appropriate saddle height. There are numerous factors to consider and the position can change over time as flexibility, strength and riding posture changes. The position is ultimately down to the bike fitter’s judgement but the final height should derived by using as much objective information as possible.
Nick Thomas is the resident bike fitter at The Endurance Coach. He is a fully qualified bike fitter and expert in lower limb mechanics, holding a BSc (Hons) in podiatry. You can contact him using the email address: email@example.com or see more about his fitting services by GOING HERE.